H2 /C12 fuel cells for power and HCl production - chemical cogeneration

ABSTRACT

A fuel cell for the electrolytic production of hydrogen chloride and the generation of electric energy from hydrogen and chlorine gas is disclosed. In typical application, the fuel cell operates from the hydrogen and chlorine gas generated by a chlorine electrolysis generator. The hydrogen chloride output is used to maintain acidity in the anode compartment of the electrolysis cells, and the electric energy provided from the fuel cell is used to power a portion of the electrolysis cells in the chlorine generator or for other chlorine generator electric demands. The fuel cell itself is typically formed by a passage for the flow of hydrogen chloride or hydrogen chloride and sodium chloride electrolyte between anode and cathode gas diffusion electrodes, the HCl increa 
     This invention was made with Government support under Contract No. DE-AC02-86ER80366 with the Department of Energy and the United States Government has certain rights thereto.

This invention was made with Government support under Contract No.DE-AC02-86ER80366 with the Department of Energy and the United StatesGovernment has certain rights thereto.

This application is a continuation of application Ser. No. 07/047,007,filed May 5, 1987 now abandoned Jan. 25, 1989.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to fuel cells, and in particular, theproduction of electricity and hydrogen chloride from the conversion ofhydrogen and chlorine gas to hydrogen and chloride ions in ahydrochloric acid or hydrochloric acid and sodium chloride solution.

A substantial industry exists in this country and worldwide for thegeneration of chlorine gas for industrial uses by electrolysis of asodium chloride electrolyte. Such plants typically additionally producesodium hydroxide or caustic soda which, has industrial applications, andhydrogen gas which, in the main, is considered a waste product andburned for release to the environment. Such chlorine generators aretypically with a cation selective membrane or porous diaphragm barrierin the electrolyte between the anode and cathode electrodes, and theelectrolyte on the anode side of the barrier, where chlorine gas isgenerated in the oxidation portion of the electrolysis reaction, must bemaintained in a slightly acidic condition in order to prevent oxygengeneration and other parasitic reactions. Typically, the acidity of theanode region is maintained by burning a small portion of the hydrogenand chlorine gases generated by the chlorine generator system in areactor from which the resulting hydrogen chloride is fed back to theanode region of the electrolysis cell or cells in the chlorinegenerator.

In U.S. Pat. No. 4,336,115 there is disclosed a system where, in theproduction of chlorine gas by electrolysis, the hydrogen and chlorine orother halogen gases are reacted in a catalytic reaction to form thecorresponding acid. In U.S. Pat. No. 3,864,236 a reversable electrolytecell is disclosed for the production of either chlorine or hydrogenchloride. Neither of these references address the loss of energyemployed in dealing with the waste products or in the hydrogen chloridegeneration for the chlorine electrolysis process.

BRIEF SUMMARY OF THE INVENTION

In accordance with the teaching of the present invention, a fuel cell isprovided for the production of hydrogen chloride and electrical energyfrom hydrogen and chlorine gases. In a typical application the hydrogenand chlorine gases are obtained by diverting a small percentage of thechlorine from a electrolysis chlorine generator along with a portion ofthe hydrogen waste stream. These are applied to the fuel cell of thepresent invention along with a dilute hydrogen chloride or dilutehydrogen chloride and sodium chloride solution. Electrical energy isproduced as an output of the electrodes of the fuel cell, and aconcentrated hydrogen chloride solution is taken as an output streamfrom the fuel cell. The thus produced hydrogen chloride is then returnedto the anode region of the electrolysis chlorine generator cells tomaintain an anode acidity that prevents the degeneration of the anodereaction into an oxygen generation. The electrical energy provided as anoutput from the fuel cell electrodes, being of a direct current nature,may typically be applied to a selected portion of the electrolysis cellsto drive the electrolysis reaction in those cells, thereby reducing theelectrical energy demand for the chlorine generator that must becommercially purchased.

The fuel cell according to the present invention in typical applicationcomprises one or more cells in which a flow of hydrogen chloride orhydrogen chloride and sodium chloride electrolyte is established betweenanode and cathode gas diffusion electrodes. Hydrogen and chlorine gasesare applied to the electrode surfaces opposite from the surfacesbordering the electrolyte solution and transport through the diffusionelectrodes, permitting the respective oxidation and reduction reactionsat the anode and cathode to proceed, increasing the hydrogen chlorideconcentration. At the end of the flow, concentrated hydrogen chloride orconcentrated hydrogen chloride and sodium chloride is removed. Theelectrodes will drive an electron flow from anode to cathode outside ofthe electrolyte solution as a result of the energy of formation of thehydrogen chloride from the anode and cathode reactions.

In order to prevent poisioning of the anode reaction by chloride ions, abarrier cation-selective membrane, typically a solid polymerelectrolyte, is placed over the anode electrode. This membrane preventsthe migration of chloride ions to the region adjacent the anodeelectrode where the hydrogen to hydrogen ion oxidation reaction takesplace.

The anode and cathode electrodes are preferably metals of catalyticactivity with respect to the oxidation and reduction reactions ofconverting hydrogen and chlorine gases to the respective ions with therespective release and absorption of electrons. For this purpose agraphitic electrode having a high microstructure surface area relativeto the geometric surface area of the electrode as a whole is typicallyemployed. Either or both electrodes may be platinum coated to achieve aplatinum loaded carbon surface structure.

The resulting fuel cell, which sacrifices reversability for efficiency,achieves a high level of effectiveness in conversion of hydrogen andchlorine into hydrogen chloride with a efficient capture of the energyof formation as an electrical output. The electrical and hydrogenchloride outputs are advantageously utilized back in the electrolysischlorine generator for anode acidification and for energy driving theHCl dissociation, but may be utilized in other applications as well.

BRIEF DESCRIPTION OF THE DRAWING

These and other features of the present invention are more fully setforth below in the solely exemplary detailed description andaccompanying drawing of which:

FIG. 1 is a systems diagram of the fuel cell of the present invention inthe application of supplying hydrogen chloride for anode acidificationand electrical energy for electrolysis to an electrolysis based chlorinegenerator;

FIG. 2 is a diagram of the structure of the fuel cell according to oneembodiment of the present invention; and

FIG. 3 is a circuit diagram indicating one form of application of theelectrical energy output of the fuel cell of the present invention forutilization in an electrolysis chlorine generator.

DETAILED DESCRIPTION

The present invention contemplates a hydrogen/chlorine fuel cell inwhich hydrogen and chlorine inputs are converted to hydrochloric acidand electrical energy outputs. In one typical application these outputsare utilized respectively to maintain acidity at the anode of anelectrolysis chlorine generator and to supplement the commerciallysupplied electrical energy used to drive the electrolysis reaction ofthe chlorine generator.

The fuel cell of the present invention, operative in relation to anelectrolysis chlorine generator, is illustrated in FIG. 1. As shownthere, an electrolysis, based chlorine generator 12 of the diaphragm ormembrane technology is shown having a central membrane 14 which dividessodium chloride and water electrolyte region 16 into first and secondchambers 18 and 20. An anode electrode 22 is placed in the chamber 18while a cathode electrode 24 is placed in the electrolyte chamber 20.Separate outputs 26 and 28 respectively of chlorine and hydrogen gas areprovided from the electrolysis cell 12. Electrical energy for drivingthe chambers 18 and 20 electrolysis reaction of the cell 12 is providedto the electrodes 22 and 24 from a power supply 30 which receivescommercially available electricity from an external power network 32.

Commercial chlorine generation by electrolysis is typically accomplishedin a plurality of cells, each one having a general form represented bythe cell 12. For purposes of the present disclosure, the plural cellsare collectively represented by the single cell 12. Such chlorinegeneration electrolysis cells are well known in the art and require nofurther description.

According to the present invention, a fuel cell 40 is provided andadvantageously cooperates with the electrolysis generator 12 to providean input 42 of hydrogen chloride for acidifying the chamber 18 in thevicinity of the anode electrode 22 to prevent the oxidation reactionthat generates chlorine from degenerating into the generation of oxygen.Additionally, electrical energy is provided by electrodes 44 and 46 ofthe fuel cell 40 which are utilized, through the power supply 30, orother means, to reduce the amount of electrical energy which must bepurchased from the external power network 32 and thereby improve thecost effectiveness of the electrolysis generator 12.

The fuel cell 40 typically comprises a plurality of fuel cell elementsof the type illustrated in FIG. 2. As shown there, an enclosure 60contains anode and cathode electrodes 62 and 64 which define betweenthem a channel or flow passage 66 through which hydrogen chlorideelectrolyte is passed from a dilute source 68 to a concentrated output70. The concentrated output 70 forms the hydrogen chloride output whichmay be utilized as the input 42 to the electrolytic cell 12 in FIG. 1.

The electrodes 62 and 64, are of a gas diffusion design. Hydrogen andchlorine gases are supplied at respective inputs 72 and 74, and aretypically portions of the outputs 26 and 28 of the electrolysis cell 12.The gas inputs 72 and 74 are applied to respective channels 76 and 78which border respective surfaces of the electrodes 62 and 64 oppositefrom the surface which faces or borders the electrolyte channel 66. Thehydrogen and chlorine gases transport across the gas diffusionelectrodes 62 and 64, creating respective oxidation and reductionreactions that result in the generation of hydrogen and chlorine ionsrespectively as well as the respective generation and consumption ofelectrons creating a potential difference between the anode and cathodeelectrode 62 and 64 of approximately one volt. This electrical energy isharnessed through a circuit 80 for the production of useful work,typically replacing some of the electrical energy otherwise requiredfrom the external power network 32 of FIG. 1.

The anode and cathode electrodes 62 and 64 are preferably formed ofmetals of catalytic activity appropriate to the respective oxidation andreduction reactions at the anode 62 and cathode 64. In one preferredembodiment, the anode and cathode are graphitic carbon and carbon,respectively, having a very high microstructure surface area throughmicrostructure surface convolutions, relative to the geometric lengthand width dimensions of the electrodes as a whole. The electrodesurfaces may be platinum loaded carbon for enhanced catalytic activityby, for example, deposition or plating the electrode surfaces where theyconfront the electrolyte in the channel 66.

Chloride ions in the electrolyte within the channel 66 will typicallymigrate to the region approximate to the anode electrode 62, where theoxidation reaction of the hydrogen gas occurs. To prevent the disruptiveeffect of this migration, a barrier membrane 82 allowing only cations topass through is typically applied to the surface of the anode electrode62 facing the channel 66 as an exemplary solution. Such a membrane istypically a solid polymer electrolyte such as NAFION 117 (a trademark ofthe Dupont Co.).

Sodium chloride may be added to the input 68 of dilute hydrogen chlorideof the fuel cell of FIG. 2. The dimensions of the fuel cell, electrodes,and their spacing, which should typically be kept in the scale ofmillimeters, are not critical but represent tradeoffs depending upon thecurrent loading in the circuit 80 desired per area of electrode, and therelative outputs of electricity and hydrogen chloride desired for theindividual fuel cell.

The utilization of such a fuel cell to increase the efficiency of anelectrolysis-based chlorine generator, in one application, isillustrated in FIG. 3. As shown there, the electrolysis chlorinegenerator is shown in typical implementation to include a plurality ofelectrolysis cells 90. The electrical output provided by one or morefuel cells 92 of the type described above is utilized to drive theelectrolysis reaction of a subset of the electrolysis cells 90 while theremaining ones of the electrolysis cells 90 are supplied with directcurrent from the main supply 94 as rectified and appropriately reducedin voltage from the network 32. As thus shown, the utilization of theelectrical output from the fuel cell of the present invention willreplace a significant portion of the electrical demand of the chlorinegenerator, making for a substantial increase in efficiency in typicalcommercial utilization. It should be noted, however, that the electricaloutput of the fuel cell operating on hydrogen and chlorine outputs or aportion of them, from the typical hydrogen generator as well as thehydrogen chloride output may be diverted to other uses. In particularthe electrical output, instead of replacing the electrical demands ofsome of the cells 90, may be utilized to drive pumps, blowers or otherprocess equipment in the typical chlorine generating plant. In addition,the fuel cell of the present invention need not be directly connected tothe hydrogen and chlorine outputs of a electrolysis generator but mayreceive the hydrogen and chlorine gas inputs by any desired means.

Accordingly it is intended not to limit the scope of the invention inany manner beyond that defined in the following claims.

I claim:
 1. A hydrogen-chlorine fuel cell in combination with a hydrogenand chlorine electrolysis generator for supplying HCl and electricityfor said electrolysis generator, comprising:an electrolysis generatorhaving chloride-containing aqueous electrolyte, at least one chlorinegenerating anode, at least one hydrogen generating cathode, and acentral membrane between said anode and cathode; a hydrogen-chlorinefuel cell for receiving hydrogen and chlorine produced by saidelectrolysis generator and for producing HCl and electrons at apotential, said fuel cell having hydrogen chloride electrolyte, ananode, and a cathode; said fuel cell further including a chloride ionbarrier located on said fuel cell anode between said anode and saidelectrolyte for preventing poisoning of said fuel cell anode by chlorideions and for promoting non-reversibility of the conversion of hydrogenand chlorine gas to hydrogen chloride electrolyte; means for supplyingto said hydrogen-chlorine fuel cell hydrogen and chlorine generated bysaid electrolysis generator; means for applying the HCl from said fuelcell to said electrolysis generator in a location proximate to said atleast one anode; a power supply having electrical current inputs andoutputs; and a driven loop for driving electrons from at least oneelectrolysis generator anode to at least one corresponding electrolysisgenerator cathode, said driven loop comprising an electrical connectionbetween an electrical current input of said power supply and at leastone electrolysis generator anode, and further comprising an electricalconnection between an electrical current output of said power supply andsaid at least one electrolysis generator cathode corresponding to saidanode; and means for supplying electrons from said fuel cell to at leastone cathode of said electrolysis generator for use in driving at least aportion of the hydrogen and chlorine generation within said electrolysisgenerator.
 2. Apparatus according to claim 1 wherein said barrier ofsaid electrolysis generator is a diaphragm or membrane.
 3. Apparatusaccording to claim 1 wherein said fuel cell includes a platinumcatalyzed chlorine gas diffusion electrode.
 4. Apparatus according toclaim 1 wherein said fuel cell includes a graphite chlorine diffusionelectrode.
 5. Apparatus according to claim 1 wherein said means forsupplying electrons from said fuel cell to at least one cathode of saidelectrolysis generator comprises a generating loop for electricallyinterconnecting said power supply to said fuel cell, said generatingloop having an electrical connection between an electrical current inputof said power supply and fuel cell anode and an electrical connectionbetween an electrical current output of said power supply and fuel cellcathode.
 6. Apparatus according to claim 1 wherein said electrolysisgenerator includes a plurality of electrolysis cells, a subset of whichare electrically connected in parallel to said power supply, anothersubset of which are electrically connected to said fuel cell. 7.Apparatus according to claim 1 wherein said fuel cell includes one ormore gas diffusion electrodes facing on one surface thereof anelectrolyte containing hydrogen chloride and exposed on another oppositesurface thereof to hydrogen or chlorine gas.
 8. The apparatus of claim 7further including:a passage adjacent said opposite surface of said oneor more gas diffusion electrodes; and means for applying hydrogen orchlorine gas to said passage.
 9. Apparatus according to claim 7 whereinthe anode of the fuel cell is a gas diffusion electrode.
 10. Apparatusaccording to claim 1 wherein said fuel cell further includes:first andsecond electrodes forming respectively fuel cell anode and cathodeelectrodes; a flow channel defined between said anode and cathodeelectrodes; and means for establishing a concentration gradient ofhydrogen chloride electrolyte along said channel in a direction parallelto said anode and cathode electrodes.
 11. Apparatus according to claim10, wherein said hydrogen chloride electrolyte includes sodium chloride.12. Apparatus according to claim 1 wherein said fuel cell includes anodeand cathode electrodes having ability to catalyze oxidation of hydrogenand reduction of chlorine respectively.
 13. Apparatus according to claim1 wherein the fuel cell for the production of hydrogen chloride andelectrons from hydrogen gas and chlorine gas, comprises:anode andcathode electrodes; an electrolyte of aqueous hydrogen chloride oraqueous hydrogen chloride plus sodium chloride placed between frontsurfaces of said anode and cathode electrodes; means for introducinghydrogen gas to said anode electrode and chlorine gas to said cathodeelectrode; and a chloride ion barrier placed on said anode electrodebetween said anode electrode and said electrolyte.
 14. The fuel cell ofclaim 13 including means for maintaining a concentration gradient ofhydrogen chloride in said electrolyte in a direction parallel to saidanode and cathode electrodes.
 15. The fuel cell of claim 13 wherein atleast one of said anode and cathode electrodes is a gas diffusionelectrode having hydrogen or chlorine gas respectively applied to asurface thereof opposite to the surface facing said hydrogen chlorideelectrolyte.
 16. The fuel cell of claim 13 wherein at least one of saidanode and cathode electrodes is graphitic, having a microstructuresurface area substantially greater than the geometric surface areathereof and provided with or without a platinum coating.
 17. A processfor driving a hydrogen-chlorine fuel cell in combination with a hydrogenand chlorine electrolysis generator, for supplying HCl and electricityfor the electrolysis generator, comprising steps of:generating hydrogenand chlorine from an electrolysis generator having chloride-containingaqueous electrolyte, at least one chlorine generating anode, at leastone hydrogen generating cathode, and a barrier between said at least oneanode and cathode; providing a fuel cell having hydrogen chlorideelectrolyte, at least one anode, and at least one cathode; receiving insaid fuel cell hydrogen and chlorine produced by said electrolysisgenerator, said fuel cell producing HCl and electrons at a potential;providing in said fuel cell a chloride ion barrier located on said atleast one fuel cell anode between said anode and electrolyte forpreventing poisoning of said anode by chloride ions and for promotingnon-reversibility of the conversion of hydrogen and chlorine gas tohydrogen chloride; applying the HCl from said fuel cell to theelectrolysis generator in a location proximate to said electrolysisgenerator anode; providing a power supply having an electrical currentinput and output for driving the hydrogen and chlorine generation insaid electrolysis generator; providing a driving loop between said powersupply and said electrolysis generator by connecting an electricalcurrent input to at least one electrolysis generator anode andconnecting an electrical current output of said power supply to anelectrolysis generator cathode corresponding to said anode; andsupplying electrons from said fuel cell to said electrolysis generatorfor use in driving the reaction of said electrolysis generator.
 18. Theprocess according to claim 17 wherein said power supply is electricallyconnected in parallel to both of said electrolysis generator and saidfuel cell.
 19. The process according to claim 17 where the process forproducing hydrogen chloride and electrons from hydrogen and chlorine gascomprises the steps of:applying a relatively dilute chloride plus sodiumchloride electrolyte solution to a channel formed between anode andcathode gas diffusion electrodes, said anode electrode having thereon achloride ion barrier between said anode electrode and said electrolyte,to impede transport of chloride ions from said electrolyte to saidanode; applying hydrogen and chlorine gas respectively to anode andcathode gas diffusion electrodes from a side opposite said channel;extracting a relatively concentrated hydrogen chloride solution from aregion between said anode and cathode electrodes remote from the pointof application of said dilute hydrogen chloride solution; and forming acircuit for a flow of electrons from said anode to said cathode externalof said electrolyte.
 20. The process according to claim 17 where theprocess for converting hydrogen and chlorine gas to hydrogen chlorideand electrons comprises the steps of:applying a relatively dilutehydrogen chloride solution to a passage formed between an anode and acathode electrode, at least said anode being a gas diffusion electrode;applying chlorine gas to said hydrogen chloride solution in the vicinityof said cathode electrode; applying hydrogen gas through said gasdiffusion anode electrode into said hydrogen chloride solution; impedingthe flow of chloride ions in said hydrogen chloride solution to saidanode electrode; extracting from said hydrogen chloride solution,hydrogen chloride of a relatively more concentrated nature from alocation remote from the place of application of said relatively dilutehydrogen chloride solution; and forming a circuit for the flow ofenergetic electrons from said anode electrode to said cathode electrodeexternal of said hydrogen chloride solution.